Web Register not working

Hello guys,
I have tried setting up web register 0.4 from phptools but I can't get it working. I host it on nginx, use PHP 5 so it works with this old application but my issue is, the page loads, I can set up admin password, but anytime I either log in or try to create an account it gets to a blank white page. If I enable warning reporting it also reports such things as "Notice: Undefined index (...) but from what I read it is not an issue.
In PHP logs etc there is no errors that could tell me what's wrong, when using PHP 7 I had additional errors about missing sql functions, but now, logs are just empty but it does not seem to be working, and I can't really tell if it is connecting to a database as well because of no logs. Is there maybe a newer version of the script available somewhere or someone can help me with this issue?